The invention relates to a process and apparatus for distributing fluidizing gas to a reactor in which hydrocarbon feed is contacted with catalyst. A field of the invention may be the field of fluid catalytic cracking (FCC).
FCC is a hydrocarbon conversion process accomplished by contacting hydrocarbons in a fluidized reaction zone with a catalyst composed of finely divided particulate material. The reaction in catalytic cracking, as opposed to hydrocracking, is carried out in the absence of substantial added hydrogen or the consumption of hydrogen. As the cracking reaction proceeds substantial amounts of highly carbonaceous material referred to as coke are deposited on the catalyst to provide coked or carbonized catalyst. This carbonized catalyst is often referred to as spent catalyst. However, this term may be misconstrued because the carbonized catalyst still has significant catalytic activity. Vaporous products are separated from carbonized catalyst in a reactor vessel. Carbonized catalyst may be subjected to stripping over an inert gas such as steam to strip entrained hydrocarbonaceous gases from the carbonized catalyst. A high temperature regeneration with oxygen within a regeneration zone operation burns coke from the carbonized catalyst which may have been stripped.
Although the carbonized catalyst carries coke deposits it may still have activity. U.S. Pat. No. 3,888,762 discloses mixing carbonized and regenerated catalyst for contact with the hydrocarbon feed. The regenerated catalyst may be in the range of 593° to 760° C. (1100° to 1400° F.) and the carbonized catalyst may be in the range of 482° to 621° C. (900° to 1150° F.). U.S. Pat. No. 5,597,537 discloses mixing the carbonized and regenerated catalyst in a blending vessel to allow the regenerated and carbonized catalyst to reach a temperature equilibrium before contacting the hydrocarbon feed. U.S. Pat. No. 7,935,314 B2 discloses baffles in the riser to obstruct upward catalyst flow to foster mixing. A mixed catalyst with more uniform temperature avoids undesirable hot spots that can generate nonselective cracking to reduce the value of the product hydrocarbons.
Inert fluidizing gas such as steam is distributed into the riser to fluidize the catalyst and to atomize the hydrocarbon feed. Fluidization of the catalyst pushes the catalyst up the riser so it can contact the hydrocarbon feed. Contact of feed and catalyst converts liquid feed to gaseous feed and gaseous feed converts to smaller gaseous products multiplying the volume of material in the riser, thereby providing additional motive force to push material up the riser. If more than one stream of catalyst is fed to the riser, the fluidization gas plays a significant role in facilitating mixing of the two streams.
Current known methods of distributing a fluidizing gas to a riser pose technical challenges. Typically, distribution would be accomplished by using a conventional steam ring distributor. However, equipment in the riser to facilitate mixing of catalyst streams makes location of a steam ring distributor cumbersome. Other known means of distributing the fluidizing gas, such as open pipes or pipes with slots at the end, are inefficient at evenly distributing the fluidizing gas the riser.
It may be desirable to provide a distributor for distributing fluidizing gas to an FCC reactor.
It may also be desirable to provide a distributor for distributing fluidizing gas to an FCC reactor that assists with mixing of separate streams of catalyst.